A touchpad, which is also known as a track pad, is an input device that includes a special surface that is capable of translating the motion and position of a user's finger to a relative position on, for example, a screen or monitor. Touchpads are becoming even more abundant on laptop computers, and also can be used as a substitute for a computer mouse when, for example, there is limited space. Touchpads vary in size but are rarely made larger than 40 square cm with their size generally being proportional to the device which with they are associated. They can also be found on personal digital assistants (PDAs), portable media players, laptops, netbooks, and the like.
In general, touchpads operate either based on capacitive sensing and/or conductance sensing. The most common technology used entails sensing the capacitance of a finger, or the capacitance between sensors. Because of the property being sensed, capacitance-based touchpads will not sense the tip of a pencil or other similar implement. Gloved fingers will generally also be problematic, and may cause problems when a user is trying to operate the device.
Touchpads, similar to touchscreens, by their design, are able to sense absolute positions, with precision being limited by their size. For common use as a pointing device, the dragging motion of a finger is translated into a finer, relative motion of a cursor on a screen—analogous to the handling of a mouse that is lifted and put back on a surface. Buttons comparable to those present on a mouse are typically below, above, or beside the touchpad with the buttons serving in a similar manner to the buttons on a mouse. Depending on the model of the touchpad and drivers behind it, one may also be able to click by tapping your finger on the touchpad and a drag with tap followed by a continuous pointing motion (a click and a half). Touchpad drivers can also allow the use of multiple fingers to facilitate functionality corresponding to the other mouse buttons, commonly a two-finger tapping is correlatable to the center button of a mouse.
Some touchpads also have “hot spots” which are locations on the touchpad that facilitate user intentions other than pointing. For example, on certain touchpads, moving the finger along an edge of the touchpad will act as a scroll wheel, controlling the scroll bar and scrolling the window that has the focus vertically or horizontally depending on which edge is stroked. Some companies use two-finger dragging gestures for scrolling on their track pads, with these typically being driver dependent functions that can be enabled or disabled by a user. Some touchpads also include tap zones which are regions whereby a tap will execute a predetermined function. For example, the function could be pausing of the media player or launching of an application.
There are two principal technologies that are used in touchpads. In a matrix approach, a series of conductors are arranged in an array of parallel lines into layers, separated by an insulator and crossing each other at right angles to form a grid. A high frequency signal is applied sequentially between pairs of lines in this two-dimensional grid array. The current that passes between the nodes is proportional to the capacitance. When a virtual ground, such as a finger, is placed over one of the intersections between the conductive layer, some of the electric field is shunted to this virtual ground point, resulting in a change in the apparent capacitance at this location.
In the capacitive shunt method, the pad senses a changing capacitance between a transmitter and a receiver that are on opposite sides of the sensor. The transmitter creates an electric field which oscillates typically between 200 and 300 khz. If a ground point, such as finger, is placed between the transmitter and receiver, some of the field lines are shunted away, thereby decreasing the apparent capacitance. These changes in capacitance are then used as input from the device.
There are also touchpads that have advanced functionality, such as letting users scroll in an arbitrary direction by touching the pad with two fingers instead of one, and then moving their fingers across the pad in the direction they wish to scroll. Other enhanced functionality includes the ability to allow users to do various combinations of gestures, such as swiping four fingers up or down to activate a particular application.
A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to a touch or to a contact to the display of the device by a finger, fingers or a hand. Touchscreens can also sense other passive objects, such as a pen. In general, any screen that allows a user to interact physically with what is shown on the display, via direct manipulation, is typically categorized as a touchscreen.
Touchscreens typically have two main attributes. The first is that the touchscreen enables one to interact with what is displayed directly on the screen, where it is displayed, rather than indirectly with a mouse or a touchpad. Secondly, a touchscreen allows a user to interact with the display without requiring any intermediate device, again, such as a stylus, mouse, or the like, that would usually be held in the hand. These devices are often seen in tablet PCs, and are also prominent in many digital appliances such as PDAs, satellite navigation devices, mobile phones, mobile entertainment devices, smart phones, video games, and the like.
There are a number of technologies that support touchscreens, such as resistive technologies, surface acoustic wave technologies, capacitive technologies, surface capacitance technologies, projected capacitance technologies, strain gauge technologies, optical imaging technologies, dispersive signal technologies, acoustic pulse recognition technologies, and coded LCD (bi-directional screen) technologies.